Reliability and minimal detectable change in foot pressure measurements in typically developing children.

Background: In pedobarography, clinically meaningful comparison of measurements within or between subjects is limited by data variability and measurement error. This study aims to determine the components of the minimal detectable change (MDC) in impulse across all foot regions and the reliability of these measures.

Methods: A convenience sample of foot pressures from 108 visits by normal, healthy subjects aged 2-17 years was studied. Each subject had three pedobarograph measurements taken per foot, with six subjects returning for a second visit for assessment of day-to-day variability. Using a five-region mask, segmental impulses were determined, and from these we obtained the coronal plane pressure index (CPPI). Inter-rater, intra-rater, and day-to-day data were analyzed using intraclass correlation coefficients (ICC) to quantify reliability. Variability of the data was analyzed to quantify the MDC.

Results: Inter- and intra-rater reliability was high for all measurements while variability was low, indicating small direct measurement error. Generally, the largest contributing factor to the MDC was day-to-day variability. Step-to-step variability was more dependent on foot segment than age although minor age-related changes were noted. Finally, the high relative variability in the CPPI and the medial mid foot impulse resulted in very high MDCs for these measures.